The present invention relates to door safety devices and more particularly to a safety system in which the door is automatically opened when it strikes an obstruction while being closed.
At the present time the use of safety edge devices on doors, to prevent the door from being closed when it meets an obstruction, is well known, particularly in the doors of automatic elevators. For example, if an elevator door should hit or approach a passenger in its doorway, the elevator door will automatically open.
Various types of systems have been suggested to control such doors. For example, a series of light beams and a series of photoelectric detectors, i.e., "electric eyes," may be used between the door and the door frame. When one of the beams is interrupted, a controlled motor operates and opens the door. Alternatively, the door edge may carry an elongated flexible gas filled bag so that, when the edge strikes an obstruction, the gas pressure rises and operates a motor control mechanism. As another alternative, various types of pressure sensitive electrical switches, such as microswitches, may be used in the door edge. The switches may directly, or indirectly through an amplifying circuit, control a motor which opens the door.
It would be desirable to use a door safety system in other types of doors, particularly in a factory environment. For example, an increased interest has developed in noise control within factories. This has resulted in an increased use of enclosures for noisy machines. Such enclosures require various types of "doors," as that term is used herein, such as vertical sliding portals, horizontal swinging portals, movable hoods and movable windows. These "doors" may be dangerous if closed upon an obstruction, such as a tool or a worker's hand.
However, the door safety systems currently in use present various difficulties, particularly if employed in a factory environment. Certain of those door safety systems are not "fail safe," that is, they will not provide protection if one, or more, of their components should fail. For example, in the case of a direct contact microswitch, the switch contacts may become corroded and fail to make electrical contact when the door hits an obstruction. Other proposed safety door edge systems may be too delicate or complicated for use in factory safety systems.